Electronic control module for anti-skid braking systems

ABSTRACT

An electronic control module for an automatic anti-skid braking system for vehicles such as automobiles. A velocity-sensing mechanism associated with a vehicle operates while the vehicle is in motion to produce a pulse train having a frequency varying in direct proportion to the rotational velocity of the rear wheels. The varying-frequency pulse train is converted to an amplitudevarying dc &#39;&#39;&#39;&#39;velocity&#39;&#39;&#39;&#39; voltage signal, also directly proportional to the rotational velocity of the rear wheels, and differentiated by a capacitor included in a differentiatoramplifier circuit to produce positive-going and negative-going voltage pulses corresponding respectively, to increases and decreases in the voltage level of the &#39;&#39;&#39;&#39;velocity&#39;&#39;&#39;&#39; voltage signal. The negative-going voltage pulses, corresponding to decreases in velocity, are then amplified and inverted by the differentiator-amplifier circuit and compared with a dc &#39;&#39;&#39;&#39;deceleration&#39;&#39;&#39;&#39; reference voltage having a value corresponding to a predetermined value of wheel deceleration existing during braking of a vehicle and indicating the imminence of a skidding or wheel lock-up situation. If the wheel deceleration of a vehicle being braked exceeds the predetermined value of wheel deceleration at any given moment, thereby indicating an impending wheel lock-up situation, and, in addition, the decelerating vehicle is traveling at a velocity exceeding a predetermined cut-out velocity below which anti-skid braking operation is not considered necessary (e.g., below five miles/hour), an output pulse is produced by the differentiatoramplifier circuit which exceeds the value of the dc &#39;&#39;&#39;&#39;deceleration&#39;&#39;&#39;&#39; reference voltage level. A load control pulse is then produced and applied to a load control circuit. The load control circuit operates in response to the load control pulse, and also to voltages from a vehicle deceleration switch associated with the vehicle, to apply to a load (e.g., a brakecontrol mechanism) control signals of either a first repetition rate or a second repetition rate for releasing the brakes of the vehicle. Control signals of the first repetition rate are applied to the load when a first voltage is produced by the deceleration switch during an impending wheel lock-up situation and control signals of the second repetition rate are applied to the load when a second voltage is produced by the deceleration switch during an impending wheel lock-up situation. The first voltage is produced by the deceleration switch when the vehicle being braked is decelerating at a rate less than a predetermined rate and, when it occurs during an impending wheel lock-up situation, indicates that the road surface on which braking is taking place has a low coefficient of friction, that is, it is a wet road surface or a snow, ice, or oil-covered surface. The second voltage is produced by the deceleration switch when the vehicle being braked is decelerating at a rate greater than the predetermined rate and, when it occurs during an impending wheel lock-up situation, indicates that the road surface on which braking is taking place has high coefficient of friction, that is, it is a dry road surface.

United .States Patent [191 Hillman,Jr.

[111 3,790,855 [45] Feb. 5, 1974 ELECTRONIC CONTROL MODULE FOR ANTI-SKIDBRAKING SYSTEMS [75] Inventor: Allen F. Hillman, Jr., Muncy, Pa.

[73] Assignee: GTE Laboratories Incorporated,

Waltham, Mass.

[22] Filed: Dec. 4, 1972 [21] Appl. No.: 311,927

[52] US. Cl. 317/5 [51] Int. CL. B60t 8/08, G0lp 15/08 [58] Field ofSearch 317/5 [56] References Cited UNITEDSTATES PATENTS 3,578,819 5/1971Atkins 317/5 3,611,109 10/1971 Jones 317/5 3,614,173 10/1971Branson.....

3,622,208 11/1971 Krugler, Jr 317/5 3,680,655 8/1972 Beyerlein et al317/5 3,710,186 l/l973 Sharp 317/5 Primary ExaminerL. T. Hix

AttomefiA gent, or Firm Irving M. Kriegsman [5 7] ABSTRACT An electroniccontrol module for an automatic antiskid braking system for vehiclessuch as automobiles. A velocity-sensing mechanism associated with avehicle operates while the vehicle is in motion to produce a pulse trainhaving a frequency varying in direct proportion to the rotationalvelocity of the rear wheels. The varying-frequency pulse train isconverted to an amplitude-varying dc velocity voltage signal, alsodirectly proportional to the rotational velocity of the corresponding toa predetermined value of wheel deceleration existing during braking of avehicle and indicating the imminence of a skidding or wheel lock-upsituation.

If the wheel deceleration of a vehicle being braked exceeds thepredetermined value of wheel deceleration atany given moment, therebyindicating an impending wheel lock-up situation, and, in addition, thedecelerating vehicle is traveling at a velocity exceeding apredetermined cut-out velocity below which anti-skid braking operationis not considered necessary (e.g., below five miles/hour), an outputpulse is produced by the differentiator-amplifier circuit which exceedsthe value of the dc deceleration reference voltage level. A load controlpulse is then produced and applied to a load control circuit. The loadcontrol circuit operates in response to the load control pulse, and alsoto voltages from a vehicle deceleration switch associated with thevehicle, to apply to a load (e.g., a brake-control mechanism) controlsignals of either a first repetition rate or a second repetition ratefor releasing the brakes of the vehicle. Control signals of the firstrepetition rate are applied to the load when a first voltage is producedby the deceleration switch during an impending wheel lock-up situationand control signals of the second repetition rate are applied to theload when a second voltage is produced by the deceleration switch duringan impending wheel lock-up situation. The first voltage is produced bythe deceleration switch when the vehicle being braked is decelerating ata rate less than a predetermined rate and, when it occurs during animpending wheel lock-up situation, indicates that the road surface onwhich braking is taking place has a low coefficient of friction, thatis, it is a wet road surface or a snow, ice, or oil-covered surface. Thesecond voltage is produced by the deceleration switch when the vehiclebeing braked is decelerating at a rate greater than the predeterminedrate and, when it occurs during an impending wheel lock-up situation,indicates that the road surface on which braking is taking place hashigh coefficient of friction, that is, it is a dry road surface.

15 Claims, 14 Drawing Figures ,PPULSE PROCESSING CIRCUlT 2 FROM '9VELOCIYV- PULSE n a... area I ASSEMBLY cmcwr FIG 9 ns CIRCUtY FIG cmcun-FIG cmcun F16 (ma) 26) 2m 2141 2w I 2w uc uEEFnIrToT j I macsngi vREFEREIgUE I l NAL FIG 2 DECELERAYKJN I f 2 1 l mmzsuow ncDIFFERENTIATOR- DECELE'W'ON I :ROCESS'NG AMPLIFIER 1 CIRCUIT FIGcowmnroe cmcun' I 4 L .1 ac VEHICL 5\ VELOCITY VELOCITY ROM cur-ourrnnzsnom seams nerr n gzg cmcun' cmcun 1 DUAL-RATE INPUT OUTPUT TO BRAKEgy ircu ,j'fi jggggt'gg SWITCH DNYROL cun' mum cmcun MECHANISM v{ I F GSzutem LOAD CONTROL CIRCUIT 6 DECELERAYION SWITCHI 15 ELECTRONIC CONTROLMODULE FOR ANTI-SKID BRAKING SYSTEMS BACKGROUND OF THE INVENTION Thepresent invention relates to electronic circuitry and, moreparticularly, to an electronic control module for use in anti-skidbraking systems for vehicles such as automobiles.

There has existed for several years a great need and demand forautomatic anti-skid braking systems for providing directional stabilityto automobiles experiencing or about to experience wheel lock-upconditions while at the same time maintaining stopping distances withinreasonable values. Various automatic anti-skid braking systems, bothelectronic and mechanical in nature, have been proposed heretofore foruse with automobiles, but for reasons such as excessive cost, weight, orcomplexity, or for reasons of poor performance or various technicalproblems, most of these anti-skid braking systems have not received widecommercial acceptance by automobile manufacturers. One anti-skid vehiclebraking system which has been used commercially includes an electroniccontrol module for determining when a rear wheel lock-up condition ispresent and for appropriately operating a brake-control mechanism tostabilize the vehicle so as to enable the operator to bring the vehicleunder control. The stimulus, or input, which is used in theabove-mentioned system for initiating operation of the brake-controlmechanism is a wheel lock-up condition. The present invention issimilarly concerned with an electronic control module for automaticanti-skid braking systems but the electronic module of the presentinvention differs significantly from the electronic control module ofthe abovementioned system in that it provides for operation of thebrake-control mechanism before a wheel lock-up situation can occur,thereby assuring earlier and more effective stabilization of a vehicleabout to experience -a wheel lock-up situation. Another significantdifference is that with the electronic control module of the presentinvention the brake-control mechanism of a vehicle being braked andabout to experience a wheel lock-up situation may be actuated at a firstrepetition rate or a second repetition rate to release the brakes andpermit the wheels to spin up, the particular rate depending on thecondition of the road surface at the time of braking, that is, whetherthe road surface has a low coefficient of friction, such as a wet roadsurface or a snow, ice, or oil-covered surface, or a high coefficient offriction, such as a dry road surface. These road surface conditions areindicated by voltages produced by a deceleration switch, such as aconventional decelerometer, during impending wheel lock-up situations.

BRIEF SUMMARY OF THE INVENTION 'Briefly, in accordance with the presentinvention, an electronic module for an anti-skid braking system isprovided for operating the brake control mechanism of a wheeled vehicle.The electronic module includes a first means operative while the vehicleis in motion to each output signal produced by the second means with thevalue of a deceleration reference signal corresponding to apredetermined value of wheel deceleration indicating the imminence of awheel lock-up condition and to produce an output signal whenever thevalue of an output signal produced by the second means bears apredetermined relationship to the value of the deceleration referencesignal.

The electronic module of the invention further includes a decelerationmeans associated with the vehicle. The deceleration means operates whenthe vehicle decelerates at a rate less than a predetermined rate toproduce a first control signal and operates when the vehicle deceleratesat a rate greater than the predetermined rate to produce a secondcontrol signal. A load control means coupled to the third means and tothe deceleration means operates in response to an output signal producedby the third means and in response to a first control signal produced bythe deceleration means to produce and apply to an output connection afirst train of output pulses having a first repetition rate. The loadcontrol means further operates in response to an output signal producedby the third means and in response to a second control signal producedby the deceleration means to produce and apply to the output connectiona second train of output pulses having a second repetition rate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic blockdiagrammatic representation of an electronic control module inaccordancewith the invention for an automatic anti-skid braking system for usewith vehicles;

FIGS. 2(a)2(j) are waveforms of electrical signals occurring at variouspoints in the electronic control module shown in FIG. 1;

FIG. 3 is a semi-schematic representation of a velocity-sensingmechanism which may be employed for providing input signals to theelectronic control module of FIG. 1;

FIG. 4 is a schematic representation of a differentiator-amplifiercircuit and comparator circuit of a preferred form which may be employedin the electronic control module of FIG. 1; and

F IG. 5 is a schematic representation of a load control circuit of apreferred form which may be employed in the electronic control module ofFIG. 1.

GENERAL DESCRIPTION OF THE INVENTION FIG. 1

Referring now to FIG. 1, there is shown an electronic control module 1for an automatic anti-skid braking system in accordance with the presentinvention. As indicated in FIG. 1, the electronic control module 1generally includes a pulse processing circuit 2, a decelerationthreshold dc signal processing circuit 3, a velocity threshold circuit4, a gating circuit 5, a load control circuit 6, and a decelerationswitch 18. The pulse processing circuit 2 further includes, in a seriesarrangement, a pulse differentiator circuit 7, a clipping circuit 8, amonostable multivibrator circuit 9, a pulse shaping circuit l0, and anac to dc converter circuit 11. As will be discussed fully hereinafter,the purpose of the pulse processing circuit 2 is to convert avarying-frequency sinusoidal pulse train received from avelocity-sensing mechanism associated with a vehicle and representativeof the variations in rotational velocity of the rear wheels of thevehicle to an amplitude-varying dc velocity voltage signal directlyproportional to the rotational velocity of the rear wheels of thevehicle.

The dc velocity voltage signal produced by the pulse processing circuit2 is applied to the deceleration threshold dc signal processing circuit3 and also to the velocity threshold circuit 4. The decelerationthreshold dc signal processing circuit 3 includes adifferentiatoramplifier circuit 12 and a deceleration thresholdcomparator circuit 13. As will also be discussed fully hereinafter inconnection with a preferred form of the deceleration threshold dc signalprocessing circuit 3, the deceleration threshold dc signal processingcircuit 3 operates to detect changes in the voltage level of thevelocity voltage signal produced by the pulse processing circuit 2.These voltage changes are amplified, and the voltage changes produced asa result of vehicle deceleration are compared with a dc decelerationthreshold reference voltage level having a value corresponding to apredetermined value of wheel deceleration existing during the braking ofa vehicle and indicating the imminence of a wheel lock-up, or skidding,condition. If the wheel deceleration of a vehicle being braked exceedsthe predetermined value of wheel deceleration at any given moment,thereby indicating an impending wheel lock-up or skidding situation, avoltage pulse is produced in the deceleration threshold dc signalprocessing circuit 3 which exceeds the value of the decelerationthreshold reference voltage level. A load control pulse is produced bythe deceleration threshold dc signal processing circuit 3 for operatingthe brake-control mechanism (not shown) of the vehicle to release thebrakes of the vehicle and to allow the rear wheels to spin up.

The load control pulse applied to the gating circuit is gated throughthe gating circuit 5 to the load control circuit 6 in response tosignals produced simultaneously by the velocity threshold circuit 4 anda conventional braking circuit (not shown). More specifically, a signalis produced and applied to the gating circuit 5 by the velocitythreshold circuit 4 when the vehicle being braked is travelling at avelocity equal to or exceeding a threshold cut-out velocity below whichoperation of the brake-control mechanism is considered unnecessary, forexample, below 5 miles per hour, and a signal is produced and applied tothe gating circuit 5 by the braking circuit during application of thebrakes by the operator. In the above fashion, automatic brake control iseffected only when the vehicle is travelling at a velocity equal to orexceeding a minimum threshold cut-out velocity and, at the same time,the brakes are being applied by the operator of the vehicle The loadcontrol circuit 6 includes, as indicated in FIG. 1, an input switchcircuit 15, adual-rate freerunning multivibrator circuit 16, and anoutput switch circuit 17. As will be described fully hereinafter inconnection with a preferred form of the load control circuit 6, the loadcontrol circuit 6 operates to cause control signals to be applied to thebrake-control mechanism of a vehicle at a first repetition rate when thevehicle at the time of braking is travelling on a road surface having alow coefficient of friction, for example, a, wet road surface, or asnow, ice, or oil-covered road surface, or control signals of asecond,-higher repetition rate when the vehicle at the time of brakingis travelling on a road surface having a high coefficient of friction,

for example, a dry road surface. The two types or road surfaceconditions are indicated by control voltages produced by thedeceleration switch 18 during impending wheel lock-up situations, afirst voltage being produced by the deceleration switch 18 when thevehicle being braked is decelerating at a rate less than a predeterminedrate, for example, less than 16 ft/sec/sec, and a second voltage beingproduced by the deceleration switch 18 when the vehicle being braked isdecelerating at a rate greater than the predetermined rate, that is,above 16 ft/sec/sec. The brake-control mechanism operates in response tothe control signals of the first repetition rate or the secondrepetition rate to alternately release and apply the brakes of thevehicle at the first rate or the second rate, respectively. At such timeas the value of the wheel deceleration no longer exceeds thepredetermined value of wheel deceleration, normal braking action on thepart of the operator is allowed to take place until such time, if any,as further brake action by the electronic control module 1 may becomenecessary or the vehicle velocity drops below 5 miles/- hour. During thetime of the operation of the brakecontrol mechanism by the electroniccontrol module 1, the operators braking action is over-ridden by theaction of the electronic control module 1. The operation of theelectronic control module 1 of FIG. 1 will now be described in detail inconjunction with the electrical waveforms of FIGS. 2(a)2( j) and inconjunction with FIG. 3.

DETAILED OPERATION FIGS. 1, 2(a)2(j), and

When a vehicle is in motion, a sinusoidal constant amplitude signalhaving a frequency varying in direct proportion to the rotationalvelocity of the rear wheels of the vehicle is produced by avelocitysensing mechanism associated with the wheels of the vehicle andapplied to the pulse differentiator circuit 7. FIG. 2(a) illustrates thewaveform of a portion of a typical sinusoidal output signal produced bythe wheel velocitysensing mechanism and applied to the pulsedifferentiator circuit 7. Although many different types of wheelvelocity-sensing mechanisms known to those skilled in the art may beused to provide a constant-amplitude, varying-frequency signal such asshown in FIG. 2(a), a particularly suitable wheel velocity-sensingmechanism is shown schematically in FIG. 3 and includes a circularslotted disc D fixedly mounted on the drive shaft S of a vehicle androtatable therewith, a fixed light source LS arranged on one side of theslotted disc, and a fixed photoresponsive device PR (e.g., a photodiode)arranged on the other side of the disc in optical alignment with thelight source. As the drive shaft S rotates, the light from the lightsource LS is chopped by the rotat- ,ing slotted disc D and the choppedlight is received by the photoresponsive device PR and converted to atrain of constant-amplitude pulse signals having a frequency varying indirect proportion to the rotational velocity v of the drive shaft S.Since both of the rear wheels of the vehicle cooperate with the driveshaft and rotate with the drive shaft, the constant-amplitudevaryingfrequency signals produced by the photoresponsive device PR mayalso be considered to represent the rotational velocity of the rearwheels.

The pulse differentiator circuit 7 operates to differentiate the leadingand trailing edge of each pulse received thereby, producing apositive-going voltage spike corresponding to the leading edge of thepulse and a negative-going voltage spike corresponding to the trailingedge of the pulse, as indicated in FIG. 2(b). The negative-going voltagespikes in the train of voltage spikes produced by the pulsedifferentiator circuit 7 are then removed by the clipping circuit 8, asindicated in FIG. 2(c), and the positive-going voltage spikes areapplied to the monostable multivibrator circuit 9. The monostablemultivibrator circuit 9 operates in response to the positive-goingvoltage spikes to produce corresponding output pulses each having apredetermined width-and amplitude, FIG. 2(d). To insure that the outputpulses produced by the monostable multivibrator circuit 9 have very fastrise and fall times, they are shaped by the pulse shaping circuit 10,FIG. 2(e). The train of output pulses provided by the pulse shapingcircuit 10, of the same frequency as the train of output pulses producedby the velocity-sensing mechanism (FIG. 3) but of a standardized pulsewidth more suitable for processing over a wide range of frequencyvariations, is then applied to the ac to do converter circuit 11. The acto do converter circuit 11 converts the train of output pulses producedby the pulse shaping circuit to a dc velocity" voltage signal having anamplitude-varying in direct proportion to the rotational velocity of thedrive shaft of the vehicle, and, therefore, the rear wheels of thevehicle. The waveform of the amplitude-varying dc velocity voltagesignal corresponding to the trains of pulses shown in FIGS. 2(a) and2(e) is shown in FIG. 2(f).'

The dc velocity voltage signal is then applied to thedifferentiator-amplifier circuit 12 and also to the velocity thresholdcircuit 4. The differentiator-amplifier circuit 12, a particularlysuitable implementation of which is shown in FIG. 4, to be described indetail hereinafter, operates to differentiate the dc velocity" voltagesignal to derive an acceleration-deceleration voltage signal includingpositive-going and negative-going voltage spikes corresponding,respectively, to increases and decreases in the value of the velocityvoltage signal. The train of bi-polar voltage spikes produced by thedifferentiator-amplifier circuit 12, shown in FIG. 2(g), thereforerepresents the expression idv/dt. After processing (e.g., amplificationand inversion) in the differentiator-amplifier circuit 12, the bi-polarvoltage spikes, FIG. 2(g), are applied to the deceleration thresholdcomparator circuit 13 and the positive-going spikes (invertednegative-going spikes) are compared therein with a constant, positive dcdeceleration reference voltage signal, also shown in FIG. 2(g), having avalue corresponding to a predetermined value of wheel decelerationexisting during the braking of a vehicle and indicating an imminentwheel lock-up, or skidding, situation. Each time that the value of anamplitied-inverted voltage spike produced by the differentiatoramplifiercircuit 12 exceeds the value of the dc deceleration" reference voltagesignal, thereby indicating an imminent wheel lock-up, or skidding,situation, a load control pulse such as shown in FIG. 2(h) is producedby the deceleration threshold comparator circuit 13 and applied as afirst input signal to the gating circuitS.

Additional signals, for gating each load control pulse produced by thedeceleration threshold comparator circuit 13 through the gatingcircuit-5 to the load coni trol circuit 6, are received by the gatingcircuit 5 from the velocity threshold circuit 4 and from the brakingcircuit. Specifically, a gating signal is produced by the velocitythreshold circuit 4 and applied to the gating circuit 5 at such time asthe value of the dc velocity" voltage signal produced at the output ofthe ac to dc converter circuit 11 and applied to the velocity thresholdcircuit 4 equals or exceeds the value of a dc vehicle velocity cutoutreference voltage signal corresponding to a particular cutout velocityof a vehicle below which it is considered unnecessary to operate thebrake-control mechanism. For example, it has been found unnecessary tooperate the brake-control mechanism to release the brakes of a vehiclefor a vehicle traveling at a velocity equal to or less than 5 miles/-hour. A second gating signal is produced by the braking circuit andapplied to the gating circuit 5 when the brakes are applied by theoperator of the vehicle. Thus, a load control pulse produced by thedeceleration threshold comparator circuit 13 is gated through the gatingcircuit 5 to the load control circuit 6 only when the velocity of thevehicle exceeds 5 miles/hour and, in addition, the brakes are applied.Assuming that the abovementioned input conditions for the gating circuit5 are satisfied, a load control pulse produced by the decelerationthreshold comparator circuit 13 is gated through the gating circuit 5 tothe input switch circuit 15 of the load control circuit 6.

As will be described in greater detail hereinafter in connection with aparticularly suitable implementation of the load control circuit 6,shown in FIG. 5, the input switch circuit 15 operates in response toeach load control pulse [FIG. 2(h)] produced by the decelerationthreshold comparator circuit 13 and gated through the gating circuit 5to produce an output signal having a fixed duration. This output signalis applied to the dualrate free-running multivibrator circuit 16 andalso to the output switch circuit 17. The dual-rate free-runningmultivibrator circuit 16 operates in response to the output signalproduced by the input switch circuit 15, and also in response to a firstdc voltage signal or a second dc voltage signal produced by the vehicledeceleration switch 18 associated with the vehicle (mounted at thecenter of gravity of the vehicle, for example), to produce an outputpulse train having a first repetition rate, or a second repetition rate,for example, as shown in FIGS. 2(i) and 2(j). The duration of an outputpulse train produced by the dual-rate free-running multivibrator circuit16 is the same as the duration of the output signal produced by theinput switch circuit 15. For the sake of clarity, the pulse trains ofFIGS. 2(i) and 2(j) are shown on an expanded scale in FIGS. 2(i) and 2(j). The abovementioned first dc voltage signal is produced by thedeceleration switch 18 when the vehicle being braked is decelerating ata rate less than a predetermined rate, for example, less than 16ft/sec/sec and, when it occurs during an impending wheel lock-upsituation, indicates that the vehicle is being braked on a road surfacehaving a low coefficient of friction, such as a wet road surface, or asnow, ice, or oil-covered surface. Thus, when the first dc voltagesignal is produced by the deceleration switch 18, the vehicle isdecelerating slowly. The second dc voltage signal is produced by thedeceleration switch 18 when the vehicle being braked is decelerating ata rate greater than the predetermined rate, that is, above 16ft/sec/sec, and, when it occurs during an impending wheel lock-upsituation, indicates that the vehicle is being braked on aroad surfacehaving a high coefficient of friction, such as a dry road surface. Thus,when the second dc voltage signal is produced by the deceleration switch18, the vehicle is decelerating rapidly.

The output pulse train produced by the dual-rate free-runningmultivibrator circuit 16, of the first repetition rate or the secondrepetition rate, is applied to the output switch circuit 17 and, withthe output switch 17 enabled by the input switch circuit 15, is invertedand gated through the output switch circuit 17 to the brakecontrolmechanism. The brake-control mechanism operates to repetitively releaseand apply the brakes of the vehicle at the first rate or the second ratefor the duration of the output signal produced by the input switchcircuit 15. The wheels of the vehicle are therefore allowed to spin up(accelerate). When the vehicle has sufficiently stabilized, normalbraking action on the part of the operator is allowed to take placeuntil further brake control by the electronic control module 1 becomesnecessary or until the velocity of the vehicle drops below miles/hour.Thus, it is apparent that the brake-control mechanism of a vehicleoperating on a road surface having a low coefficient of friction at thetime of braking is operated at a different rate [FIG. 2(i)] than thebrake-control mechanism of a vehicle operating on a road surface havinga high coefficient of friction at the time of braking [FIG. 2(j)]. Thisdualrate operation therefore permits the operation of the brake controlmechanism to be tailored to the particular existing road surfaceconditions.

DIFFERENTIATOR AMPLIFIER, COMPARATOR, AND LOAD CONTROL CIRCUITS FIGS. 4AND 5 Each of the abovedescribed circuits comprising the electroniccontrol module 1 of FIG. 1 may be implemented by a variety ofconventional circuits well known to those skilled in the art. However,particularly suitable and novel implementations of the decelerationthreshold dc signal processing circuit 3 and the load control circuit 6are illustrated in FIGS. 4 and 5, respectively.

As shown in FIG. 4, the differentiator-amplifier circuit 12 included inthe deceleration threshold dc signal processing circuit 3 includes alinear differential amplifier A1. The linear differential amplifier A1,which may be one of several well-known commercially availableoperational amplifiers, includes, in a conventional fashion, aninverting input terminal 20, a non-inverting input terminal 21, aninverting bias terminal 22, a noninverting bias terminal 23, acommon-point terminal 24, and an output terminal 25. The inverting inputterminal 20 is coupled to a signal-receiving input terminal 30 via acapacitor C1, and the non-inverting input terminal 21 is coupled bymeans of a coupling resistor R1 to the juncture of a pair of resistorsR2 and R3. The remote end of the resistor R2 is connected directly tosystem ground potential (e.g., the chassis of the vehicle) and theremote end of the resistor R3 is connected directly to the positiveterminal of a voltage regulating circuit 31. As is evident from FIG. 4,the resistors R2 and R3 are arranged in a voltage-divider configuration.In addition to the above-mentioned connections, the inverting biasterminal 22 is directly connected to ground potential, the non-invertingbias terminal 23 is connected directly to the positive terminal of thevoltage regulating circuit 31, and the common-point tenninal 24 isconnected directly to the juncture of the voltage divider resistors R2and R3. The desired value of gain of the linear differential amplifierA1 is achieved in a conventional manner by means of a feedback resistorR4 of appropriate value connected between the inverting input terminal20 and the output terminal 25. Frequency stability of the lineardifferential amplifier A1 is achieved in a conventional manner by acapacitor C2 of appropriate value also connected between the invertinginput terminal 20 and the output terminal 25.

The comparator circuit 13 of FIG. 4, like the differentiator-amplifiercircuit 12, also includes a linear differential amplifier. As indicatedin FIG. 4, a second linear differential amplifier A2 is provided havinga non-inverting input terminal 35, an inverting input terminal 36, aninverting bias terminal 37, a non-inverting bias terminal 38, acommon-point terminal 39, and an output terminal 40. For most effectiveoperation, it is preferable that the linear differential amplifier A2 beof the same design as the linear differential amplifier A1. Thenon-inverting input terminal 35 of the linear differential amplifier A2is coupled to the output terminal 25 of the linear differentialamplifier A1 via a pair of series-connected resistors R5 and R6. Aresistor R7 is connected between the juncture of the resistors R5 and R6and ground potential and forms a voltage divider with the resistor R6for providing voltage overload protection for the linear differentialamplifier A2. The resistor R5 serves as a current-limiting resistor.

The inverting input terminal 36 of the linear differential amplifier A2is coupled by means of a currentlimiting resistor R8 to a seriesresistive reference voltage-setting arrangement 45 including a variableresistor R9, a resistor R10 connected between one end of the variableresistor R9 and ground potential, and a resistor R11 connected betweenthe other end of the variable resistor R9 and the positive terminal ofthe voltage regulating circuit 31. The reference voltage-settingarrangement 45 serves to provide a dc deceleration threshold voltage tothe inverting input terminal 36 of the linear differential amplifier A2.In addition to the above connections, the inverting bias terminal 37 ofthe linear differential amplifier A2 is connected directly to groundpotential, the non-inverting bias terminal 38 is connected directly tothe positive terminal of the voltage regulating circuit 31, and thecommon-point terminal 39, like the common-point terminal 24 of thelinear differential amplifier A1, is connected directly to the junctureof the voltage-divider resistors R2 and R3. The output of the lineardifferential amplifier A2 is taken at the output terminal 40.

The voltage regulating circuit 31 shown in FIG. 4 may be implemented bya variety of well known circuits. However, a preferred form of thevoltage regulating circuit 31 for use in the present invention includescircuitry for converting the positive-voltage output of a standardl2-volt automobile battery, which voltage output may vary over a rangeof about 8-15 volts, to a lower, regulated value suitable for use withthe linear differential amplifiers A1 and A2, for example, 6.2-6.8volts. A particularly suitable voltage regulating circuit whichsatisfies the above requirements is described in detail and also claimedin a co-pending patent application of Lucian F. Emerson, Ser. No. 311,929, filed concurrently herewith, entitled Voltage Regulating Circuit,and assigned to the same assignee as the present application. Referencemay be made to the abovementioned co-pending application for specificdetails.

The deceleration threshold dc signal processing circuit 3 of FIG. 4operates in the following manner. In the quiescent operating state ofthe deceleration threshold dc signal processing circuit 3; that is, withno signal present at the input terminal 30, a positive input voltagesignal V having a value relative to ground potential of n/(R2 R3) (Vwhere V is the value of the positive voltage from the voltage regulatingcircuit 31, is present at the noninverting input terminal 21 of thelinear differential amplifier A1 due to the voltage divider resistors R2and R3. With the above input condition at the noninverting inputterminal 21, a positive output voltage signal V equal to V is presentedby the linear differential amplifier A1 at the output terminal 25 andalso to the inverting input terminal 20 via the feedback resistor R4.Accordingly, both of the input terminals 20 and 21 are at the samevoltage in the quiescent operating state.

The output voltage signal VAumm at the output terminal 25 of the lineardifferential amplifier A1 is applied to the voltage divider resistors R6and R7 and a positive voltage signal V having a value relative to groundpotential of R (VAKOUD),

is presented to the non-inverting input terminal 35 of the lineardifferential amplifier A2 due to the voltage divider resistors R6 andR7. A constant, positive dc reference voltage signal is applied by theresistive reference voltage-setting arrangement 45 to the invertinginput terminal 36 of the linear differential amplifier A2. The value ofthe positive dc reference voltage signal applied to the inverting inputterminal 36 of the linear differential amplifier A2 during the quiescentoperating state is established to be the same as the value of thevoltage signal A present at the non-inverting input terminal 35. Thiscondition is achieved by appropriately controlling the value of thevariable resistor R9. With both of the input terminals 35 and 36 at thesame voltage, the linear differential amplifier A2, which is connectedto operate as a differential voltage comparator, detects no differencebetween the two input voltage signals and, therefore, causes the voltageat the output terminal 40, V to be at volts.

The non-quiescent operating state of the deceleration threshold dcsignal processing circuit 3, that is, with a signal lFlG. 2(f)] from theac to dc converter circuit 11 (FIG. 1) present at the input terminal 30,is as follows. The amplitude-varying dc velocity voltage signal producedby the ac to dc converter circuit 11 (FIG. 2(f)] and applied to theinput terminal 30 is differentiated by the capacitor C1 to detectinstantaneous .changes in the amplitude of the velocity voltage signal.A positive-going voltage spike is produced by the capacitor C l inresponse to each increase in the level of the velocity" voltage signal(indicating an increase in vehicle velocity) and a negative-goingvoltage spike is produced by the capacitorCl in response to eachdecrease in the level of the velocity voltage signal (indieating adecrease in vehicle velocity). The amplitude of each voltage spikeproduced by the capacitor C1 depends on the amount of change detected bythe capacitor Cl and is directly related thereto. Each voltage spikeproduced by the capacitor C1 is applied to the inverting input terminal20 of the linear differential am-' plifier A1. As in the quiescentoperating state of the deceleration threshold dc signal processingcircuit 3, a dc voltage signal V, having a value relative to groundpotential of is applied to the non-inverting input terminal 21 of thelinear differential amplifier A1 by the voltage divider resistors R2 andR3, and also to the inverting input terminal 20 via the output terminal25 and the feedback resistor R4. Since the bi-polar voltage spikesproduced by the capacitor C1 ride on the dc voltage signal V, present atthe non-inverting input terminal 20, voltage differences are establishedbetween the input signals applied to the input terminals 20 and 21 andthe linear differential amplifier Al accordingly operates to amplify andinvert the bi-polar voltage spikes applied to the inverting inputterminal 20. The amplified and inverted bi-polar voltage spikes arepresented at the output terminal 25 of the linear differential amplifierA1.

Each output voltage spike presented at the output terminal 25 of thelinear differential amplifier A1, designated V is applied to thejuncture of the voltage divider resistors R6 and R7 and a fractionalportion thereof, equal to is applied to the non-inverting input terminal35 of the linear differential amplifier A2 [FlG. 2(g)]. A constant,positive dc reference voltage signal [FIG. 2(g)], of the same value asestablished for the quiescent operating state of the decelerationthreshold dc signal processing circuit 3, is applied to the invertinginput terminal 36 by the resistive reference voltage'setting arrangement45. The linear differential amplifier A2 operates to compare eachpositive-going voltage spike presented to the non-inverting inputterminal 35 with the constant, positive dc reference voltage signal andto produce a positive maximum-gain load control pulse [FlG. 2(h)],measured relative to ground potential, when the value of apositive-going voltage spike exceeds the value of the constant, positivedc reference voltage signal. No load control pulse is produced fornegative-going voltage spikes applied to the noninverting input terminal35 inasmuch as the inverting bias terminal 37 is at ground potentialand, therefore, prevents negative-going voltage spikes from driving thelinear differential amplifier A2. The output produced by the lineardifferential amplifier A2 in response to each negative-going voltagespike at the non-inverting input terminal 35 is thus at 0 volts. Eachpositive maximum gain load control pulse produced by the lineardifferential amplifier A2 at the output terminal 40 [FlG. 2(h)] inresponse to a positive-going voltage spike presented to thenon-inverting input terminal 35 is applied to the gating circuit 5 foradditional processing, as briefly described hereinbefore and as will bedescribed in greater detail hereinafter.

The abovedescrib ed deceleration threshold dc signal processing circuit3 of FIG. 4 is described and also claimed in a co-pending patentapplication of Lucian F. Emerson, Ser; No. 311,928, filed concurrentlyherewith, entitled DC Signal Processing Circuit, and assigned to thesame assignee as the present application.

Referring now to FIG. 5, there is shown in detail the load controlcircuit 6 which, as mentioned before, includes the input switch circuit15, the dual-rate freerunning multivibrator l6, and the output switchcircuit 17. As shown in FIG. 5, the input switch circuit 15 includes adiode D, a capacitor C10, a resistor R20, an input npn transistor Q0,and a pull-down resistor R21. The diode D is connected at its anodeelectrode to the gating circuit 5 and at its cathode electrode to oneend of the capacitor C10. The other end of the capacitor C10 isconnected directly to ground potential. The resistor R20 is connected tothe juncture of the diode D and the capacitor C10 and to the base of thetransistor Q0. The emitter of the transistor O is connected directly toground potential, and the collector is connected through the resistorR21 to the emitter of a pnp transistor Q3 provided within the dual-ratefreerunning multivibrator circuit 16. In the operation of the timingswitch circuit 15, each positive load control pulse [FlG. 2(h)] producedby the deceleration threshold comparator circuit 13 and gated throughthe gating circuit 5 passes through the diode D and charges thecapacitor C10. When the capacitor C is charged to a value of voltagesufficient to forward bias the transistor Q0, the transistor Q0 conductsand places the emitter of an npn transistor Q1 included in the dual-ratefree-running multivibrator circuit 16 at essentially ground potential.As will be described hereinafter, this latter operation of thetransistor Q0 initiates multivibrator action on the part of thedual-rate free-running multivibrator circuit 16. Once the transistor Q0has been operated in its conducting condition and after termination ofthe load control pulse, the capacitor C10 is able to discharge to groundpotential via the resistor R20 and the conducting transistor Q0. Therate at which the capacitor C10 discharges is a function of the valuesof the capacitor C10 and the resistor R20. As the capacitor C10discharges to a level no longer able to forward bias the transistor Q0,the transistor Q0 becomes increasingly non-conducting and when thetransistor 00 becomes completely non-conducting the operation of thedual-rate free-running multivibrator circuit 16 terminates.

The dual-rate free-running multivibrator circuit 16 of FIG. 5 includesthe aforementioned npn transistor Q1 and a similar npn transistor Q2which, as is evident from FIG. 5, are interconnected in a commonfreerunning multivibrator configuration. More specifically, the base ofthe transistor O1 is coupled through a commutation resistor R25 to thecollector of the transistor 02, and the collector is coupled through aload resistor R26 to a source of positive dc voltage B+. The emitter ofthe transistor O1 is connected directly to the collector of the inputtransistor 00 provided within the input switch circuit 15. In a mannersimilar to the transistor Q], the base of the transistor O2 is coupledthrough a commutation resistor R27 to the collector of the transistorQ1, and the collector is coupled througha load resistor R28 to thesource of positive dc voltage B+. The collector of the transistor O2 isalso connected to an output terminal 45 to which output pulses producedat the collector of the transistor Q2 are applied. The emitter of thetransistor O2 is connected directly to ground potential. In addition tothe abovementioned circuit components, and as is also common infreerunning multivibrator circuits, a capacitor C12 is con-' nectedbetween the collector of the transistor 01 and the base of thetransistor Q2, and a capacitor C14 is similarly connected between thecollector of the transistor Q2 and the base of the transistor Q1.

The dual-rate manner of operation of the multivibrator circuit 16 bywhich first and second trains of output pulses having differentrepetition rates are produced at the output terminal 45 of themultivibrator circuit 16 is achieved by establishing two sets of timeconstants for controlling the operation of the transistors Q1 and Q2,and, therefore, the off and on times for the transistors Q1 and Q2. Thiscontrol of the RC time constants and the off/on times of the transistorsQ1 and Q2 is accomplished by the inclusion in the mulivibrator circuit16 of a pair of variable-resistance arrangements 46 and 47. As shown inFIG. 6, the variable-resistance arrangement 46 includes a pair ofresistors R29 and R30 connected in series with the source of positive dcvoltage B+ and the capacitor C12, and a pnp transistor Q3 connected inparallel with the resistor R29 via its emitter and collector. The baseof the transistor O3 is coupled through a current-limiting resistor R31to the deceleration switch 18. In a similar fashion as described above,the variable-resistance arrangement 47 includes a pair of resistors R32and R33 connected in series with the source of positive dc voltage 13+and the capacitor C14, and an npn transistor Q4 connected in parallelwith the resistor R32 via its collector and emitter. The base of thetransistor Q4 is coupled through a current-limiting resistor R34 to thedeceleration switch 18. The dualrate free-running multivibrator circuit16 further in cludes a resistor R35 connected between the resistor R31and ground potential and a capacitor C15 connected between the resistorR34 and ground potential. The purpose of the resistor R35 is to preventthe transistor Q3 from being overdriven, and the purpose of thecapacitor C15 is to prevent the two transistors Q3 and Q4 from operatingin their on states concurrently in the event of chattering" of thedeceleration switch 18.

The deceleration switch 18, as employed in the present invention, iscapable of supplying a dc voltage to the multivibrator circuit 16 havinga first value, for example, 0 volts dc, when a wheel lock-up conditionis imminent on a low coefficient of friction road surface,

and a second iniiiie'fbr example, 4 6 volts dc, when a wheel lock-upcondition is imminent on a high coefficient of friction road surface. Atypical value of the positive dc voltage B+ which may be used with thetwo values of voltage produced by the deceleration switch 18 is +6volts. The operation of the dual-rate free-running multivibrator circuit16 is as follows. I

In the quiescentmode of operation of the dual-rate multivibrator circuit16, that is, with the transistor Q0 in its non-conducting condition, theemitter of the transistor Q1 is open circuited, and the transistor Q1operates in its non-conducting, or off," state. With the transistor Q1operating in its non-conducting state, the voltage at its collector isat essentially the voltage 8+ and the voltage at the base of thetransistor Q2 at this time is sufficient to forward bias the transistorQ2 into its conducting, or on, state, causing the collector of thetransistor O2 to be at essentially ground potential (approximately 0volts). The collector of the transistor Q2 remains at essentially groundpotential until the transistor Q0 is operated in itsconductingcondition.

.I conducting state.

With the abovedescribed quiescent operating states for the transistorsQ1 and Q2, the collector side of the capacitor C12 is at a high value ofvoltage (at essentially 8+), and the other side, by virtue of itsconnection to the base of the conducting transistor O2, is at a lowvalue of voltage (at essentially ground potential). Similarly, thecollector side of the capacitor C14 is at a low value of voltage, byvirtue of the transistor Q2 being in its conducting state, and the otherside, by virtue of its connection to the base of the non-conductingtransistor Q1, is at a high value of voltage. These voltage conditionsaffecting the capacitors C12 and C14 cause voltages of essentially equalvalue to be established across the capacitors C12 and C14 in preparationfor initiating multivibrator action once the transistor O is operated inits conducting condition. Specifically, a charge path exists forcharging the capacitor C12 which includes the source of positive dcvoltage 8+ and the load resistor R26, and a charge path exists forcharging the capacitor C14 which includes the source of positive dcvoltage B+ and the resistors R32 and R33. The time required for chargingeach of the capacitors C12 and C14 is determined principally by thevalues of the aforementioned resistors R32 and R33, and the values ofthe capacitors C12 and C14.

To produce a train of output pulses at the output terminal 45 of themultivibrator circuit 16, the transistor Q0 must be operated in itsconducting condition and a first or second value of dc voltage must bereceived from the deceleration switch 18. When the deceleration switch18 produces its O-volt signal, zero volts are supplied to themultivibrator circuit 16 and the multivibrator circuit 16 operates toproduce output pulses at the output terminal 45 having a first ratio ofoff/on times, that is, a first repetition rate; when the decelerationswitch 18 produces its +6-volt signal, +6 volts are supplied to themultivibrator circuit 16 and the multivibrator circuit 16 operates toproduce output pulses at the output terminal 45 having a second ratio ofoff/on times, that is, a second repetition rate. Assuming initially thatthe transistor Q0 has been operated in its conducting condition by aload control pulse from the deceleration threshold circuit 13 and thatthe deceleration switch 18 is producing its 0-volt signal, the operationof the multivibrator circuit 16 may be explained as follows.

With the transistor Q0 operating in its conducting condition, theemitter of the transistor O1 is placed at ground potential wherebymultivibrator action is initiated. Specifically, with the emitter of thetransistor Q1 placed at ground potential, the voltage earlierestablished across the capacitor C14 (before the transistor Q0 conducts)is applied to and acts at the base of the transistor Q1. This voltage ispositive and of sufficient value to initiate forward biasing thetransistor Q1 into its conducting (on) state. As the transistor O1 isinitially biased into its conducting state, the capacitor C12discharges, causing a negative voltage spike to be applied to the baseof the transistor Q2. This negative voltage spike reverse biases thetransistor Q2 into its non-conducting (off) state, resulting inlanincrease in the collector voltage of the transistor Q2 in a positivedirection. This collector voltage is coupled via the com- -mutationresistor R25 into the base of the transistor Q1 and causes thetransistor Q1 to operate more fully in its With the transistor Q2operating in its nonconducting state and the transistor Q1 operating inits conducting state, the capacitor C12 is gradually charged to avoltage level for again forward biasing the transistor Q2 into itsconducting state. The charge path of the capacitor C12 at this timeincludes the source of positive dc voltage 8+ and the effectiveresistance of the variable-resistance arrangement 46. The effectiveresistance of the variable-resistance arrangement 46 is determined atthis time by the state of the deceleration switch 18. Specifically, withthe deceleration switch 18 in its 0-volt producing state, as assumedhereinabove, a zero-voltage condition is established at the base of thepnp transistor Q3. Since the emitter of the transistor Q3 is at apositive voltage (+B) with respect to the base, the transistor O3 isforward biased into its conducting state. While in the conducting state,the transistor Q3 shunts the resistor R29 and thereby establishes aneffective resistance for the variable-resistance arrangement 46 having avalue equal to the value of the resistor R30. Thus, the capacitor C12 ischarged at this time through the un-shunted resistor R30 and not throughthe series combination of resistors R29 and R30. (A small amount ofadditional voltage is developed across the capacitor Cl2 at this time byvirtue of current flow through the load resistor R26 and the commutationresistor R27, but the value of this additional voltage is negligiblewhen compared with the value of voltage developed across the capacitor C12 by virtue of current flow through the resistor R30). It is to benoted that as the above operations involving the capacitor C12 and thevariable-resistance arrangement 46 take place, the npn transistor Q4provided in the other variable-resistance arrangement 47 is not operatedin its conducting state, that is, it is reverse biased, by virtue of itsemitter being at a positive voltage greater than 0 volts.

When the value of the voltage across the capacitor C12 increases to thevalue of the forward-bias voltage of the transistor Q2, the transistorQ2 once again starts to operate in its conducting state. As thetransistor Q2 starts to operate in its conducting state and itscollector voltage starts to drop to its low value, the capacitor C14discharges, causing a negative voltage spike to be applied to the baseof the transistor Q1. This negative voltage spike serves to reverse biasthe transistor O1 in its non-conducting state and to cause the voltageat the collector of the transistor Q1 to increase in a positivedirection. The collector voltage of the transistor O1 is coupled intothe base of the transistor Q2 (via the commutation resistor R27) andcauses the transistor Q2 to operate more fully in its conducting state.The capacitor C14 is then gradually charged again, via a charge pathincluding the source of positive dc voltage B+ and the resistors R32 andR33, until the voltage across the capacitor C14 reaches the forward biasvoltage of the transistor Q1. This charging operation thereforedetermines the off time for the transistor Q1. When the voltage acrossthe capacitor C14 reaches the forward bias voltage of the transistor Q1,the transistor Q1 starts to operate again in its conducting state,thereby initiating the turn off of the transistor Q2. The abovedescribedoperation of the multivibrator circuit 16 continues until such time asthe transistor Q0 operates in its nonconducting condition at which timethe multivibrator action of the multivibrator circuit 16 is terminated.

It is evident from the abovedescribed discussion, therefore, that withthe deceleration switch 18 in its volt producing state, the off time ofthe transistor Q1 and the on time of the transistor Q2 are eachdetermined essentially by the values of the resistors R32 and R33 andthe capacitor C14 and the on time of the transistor Q1 and the off timeof the transistor Q2 are each determined essentially by the value of theresistor R30 and the capacitor C 12. As the above-describedmultivibrator action takes place, a train of output pulses of a firstrepetition rate is produced at the collector of the transistor Q2 and,thus, at the output terminal 45. This train of output pulses is appliedvia a current-limiting resistor R37 to the base of an npn transistor Qprovided in the output switch circuit 17. With the emitter of thetransistor Q5 at essentially ground potential, due to the conduction ofthe transistor Q0, the train of output pulses produced by the dual-ratefile-running multivibrator 16 is inverted by the transistor Q5 andapplied to the brake control mechanism. The configuration of the trainof output pulses produced at the collector of the transistor Q5, withthe deceleration switch 18 in its O-volt producing state is shown inFIG. 2(i) (in expanded scale).

The operation of the multivibrator circuit 16 when the decelerationswitch 18 is in its 6-volt producing state is essentially the same asthat described hereinabove. However, in this case, the transistor Q4 isforward biased into its conducting state, by virtue of the voltage atits base being sufficiently positive (approximately +6 volts) withrespect to the emitter, and the transistor O3 is reverse biased in itsnon-conducting state, by virtue of the value of voltage at its base(approximately +6 volts) being essentially equal to the value of thevoltage (e.g., +6 volts) at its emitter. With the transistor Q4operating in its conducting state, the resistor R32 is shunted wherebythe unshunted resistor R33 serves as the principal charging resistor forthe capacitor C14. In the present case, therefore, the off time of thetransistor Q1 and the on time of the transistor Q2 are each determinedessentially by the values of the resistor R33 and the capacitor C14, andthe on time of the transistor Q1 and the off time of the transistor Q2are each determined essentially by the values of the resistors R29 andR30 and the capacitor C12. A train of output pulses of a secondrepetition rate is produced at the collector of the transistor Q2 and,thus, at the output terminal 45'. This train of output pulses isinverted by the transistor Q5 and applied to the brake controlmechanism. The configuration of the train of output pulses, with thedeceleration switch 18 in its 6-volt producing state, is shown in FIG..2( j) (in expanded scale).

It is clear, therfore, that by the appropriate selection of values forthe resistors R29, R30, R32 and R33 and .for the capacitors C12 and C14,the off/on times of the pulses produced at the collector of thetransistor Q5 of the output switch circuit 17 may be made to have avariety of difierent possible values. As a result, pulse trains havingdifferent repetition rates may be readily achieved. The abovedescribeddual-rate free-running multivibrator circuit 16, with slightmodification, is described and also claimed in a co-pending applicationof herewith, entitled Dual-Rate Multivibrator Circuit,

and assigned to the same assignee as the present appli-' cation.

While there has been shown and described what is consideted a preferredembodiment of the invention, it will be obvious that various changes andmodifications may be made therein without departing from the inventionas called for in the appended claims.

What is claimed is:

1. An electronic module for an anti-skid braking systern for operatingthe brake control mechanism of a wheeled vehicle, comprising:

first means operative while the vehicle is in motion to provide avelocity signal representative of the rotational velocity of at leastone wheel of the vehicle;

second means coupled to the first means and operative to detectdecreases in the value of the velocity signal produced by the firstmeans and to produce output signals corresponding to the decreases;

third means coupled to the second means and operative to compare thevalue of each output signal produced by the second means with the valueof a deceleration reference signal corresponding to a predeterminedvalue of wheel deceleration indicating the imminence of a wheel lock-upcondition and to produce an output signal whenever the value of anoutput signal produced by the second means bears a predeterminedrelationship to the value of the deceleration reference signal;deceleration means associated with the vehicle and operative when thevehicle decelerates at a rate less than a predetermined rate to producea first control signal and operative when the vehicle decelerates at arate greater than the predetermined rate to produce a second controlsignal; and load control means coupled to the third means and to thedeceleration means and having an output connection adapted to be coupledto the brake control mechanism of the vehicle, said load control meansbeing operative in response to an output signal produced by the thirdmeans and in response to a first control signal produced by thedeceleration means to produce and apply to the output connection thereofa first train of output pulses having a first repetition rate, andoperative in response to an output signal produced by the third meansand in response to a second control signal produced by the decelerationmeans to produce and apply to the output connection thereof a secondtrain of output pulses having a second repetition rate. 2. An anti-skidbraking system in accordance with claim 1 wherein:

the deceleration means includes a decelerometer. 3. An electronic modulein accordance with claim 1 wherein: Y

the load control means includes a dual-rate multivibrator circuit. 4. Anelectronic module in accordance with claim 1 wherein the load controlmeans includes:

input means coupled to the third means and operative to receive eachoutput signal produced by the third means, said input means beingoperative in response to each output signal produced by the third meansto produce a corresponding output signal of a predetermined duration;and dual-rate multivibrator circuit means coupled to the input means andto the deceleration means and operative to receive each output signalproduced by the input means and the first and second control thedeceleration means to produce a first train of output pulses having afirst repetition rate for the duration of the output signal produced bythe input means, and operative in response to an output signal producedby the input means and a second con- 10. An electronic module foroperating the brake control mechanism of a wheeled vehicle, comprising:

first means operative while the vehicle is in motion to provide avelocity signal representative of the rotational velocity of at leastone wheel of the vehicle;

second means coupled to the first means and operative to detectdecreases in the value of the velocity signal produced by the firstmeans and to produce tl'Ol signal produced the deceleration means tooutput ignals orresponding to the decreases; l a FP of Output Ph havlhga velocity circuit means coupled to the first means and i h ip e l t h0f the operative when the velocity signal produced by the P" slgha P y 6p meahsfirst means has a value greater than a predeter- A n electronicmodule in accordance with claim 4 is mined value corresponding to apredetermined w ereln' out velocity to produce an output signal, f "Q" ah :1 f lh l i 5 braking circuit means operative to produce an output n eec ronlc mo u e m accor ance w1t 0 arm signal whenever the vehicle isbeing braked, wherein the load control means further includes: thirdmeans Coupled to the second means and (were output means coupled to themput means and to h tive to compare the value of each output signalprodual-rate multivibrator circuit means and operative duced by theSecond means with the value of a fi sssgf zsr aggg gifi 5: 11:5 gr h gceleration reference signal corresponding to a prethe dual ratemultivibrator :ircdit mea ils s a i d out dhetermined of g dicelerationindicating t e imminence o a w eel oc -u condition and to put "P bemgoperatwe response to each produce an output signal wheneyer the value ofan put slgna produced by the mput means and a train out ut si nalroduced b the second means bears of output pulses produced by thedual-rate multivie fi e d relatieiehip to the value of the bratorcircuit means to invert and apply the train deceleration referenceSigner of Output puises to an (.mtput connectlqn' gating means coupledto the velocity circuit means, 7. An electronic module in accordancewith claim 1 h b d h d wherein t 3 ra mg circuit means, an to t e t 1rmeans i l the wheel of the vehicle lS a rear wheel of the vehicle; anoperative to recellle output h S pro and duced by said means, saidgating means being operthe first means includes a wheel velocity-sensingatwe only h h to output slgnals P F by the velocity circuit means andthe braking cirmeans associated with the rear wheel of the vehicle it tt th th h a t t Si 1 and operative while the vehicle is in motion toprocu means 0 ga ere mug n ou pu gna produced by the third means; duce apulse train having a frequency varying in difeet proportion to th erotational velocity of th e deceleration means associated with thevehicle and rear wheel operative when the vehicle decelerates at a rate8. An electronic module in accordance with claim 7 less thahhpredetermmeh rate to produce, a first wherein: 40 control signal andoperative when the vehicle dethe first means further includes meanscoupled to the celerates at a rate greater than wheel velocity-sensingmeans and operative to conrate to produce a Second control g and vertthe pulse train produced by the wheel velocityload comm] meahh coupledto the gahhg means and sensing means into a dc velocity signal having ans to the qecelerahoh means and havmg an output amplitude varying inaccordance with variations in 4 cohhechoh adaPted to he h to the brakethe frequency of the pulse train produced by th Control mechanism of theveh1cle,sa1d load control whee] veloeityeensing meme means beingoperative in response to an output sig- 9. An electronic module inaccordance with claim 7 gated h the thlrd means through h gatingwherein; means and in response to a first control signal prothe vehicleincludes a drive shaft cooperating with duced by the decelerahoh hleahsto P h h the rear wheel f the vehicle; and apply to the outputconnection thereof a first tram the wheel veloeity sensing meanscomprises; of output pulses having a first repetition rate, and aslotted disc adapted to be fixedly mounted on the Operahve h response toan P? signal gated drive shaft of the vehicle and adapted to rotate fromthe thlrd means through the gatlhg means and in response to a secondcontrol signal produced by the deceleration means to produce and applyto the output connection thereof a second train of output pulses havinga second repetition rate. 11. An anti-skid braking system in accordancewith claim 10 wherein:

the deceleration means includes a decelerometer. 12. An electronicmodule in accordance with claim 10 wherein:

the load control means includes a dual-rate multivibrator circuit. 13.An electronic module in accordance with claim 10 wherein the loadcontrol means includes:

with the drive shaft;

a light source adapted to be arranged on one side of the slotted disc,said slotted disc operating to chop light produced by the light sourceat a frequency varying in accordance with variations in 6 the rotationalvelocity of the drive shaft; and

a photoresponsive device on the other side of the slotted disc inoptical alignment with the light source and operative to receive thelight chopped by the slotted disc and to convert the chopped light to atrain of pulse signals having a frequency varying in accordance with thevariations in the rotational velocity of the drive shaft.

input means coupled to the third means and operative to receive eachoutput signal produced by the third means, said input means beingoperative in response to each output signal produced by the third meansto produce a corresponding output signal of a predetermined duration;and

dual-rate multivibrator circuit means coupled to the input means and tothe deceleration means and operative to receive each output signalproduced by 20 produce a second train of output pulses having a secondrepetition rate for the duration of the output signal produced by theinput means. 14. An electronic module in accordance with claim 13wherein:

the input means and the first and second control the deceleration meansincludes a decelerometer. 15. An electronic module in accordance withclaim 13 wherein the load control means further includes:

output means coupled to the input means and to the dual-ratemultivibrator circuit means and operative to receive each output signalproduced by the input means and each train of output pulses produced bythe dual-rate multivibrator circuit means, said output means beingoperative in response to each output signal produced by the input meansand a train of output pulses produced by the dual-rate multivibratorcircuit means to invert and apply the train of output pulses to anoutput connection.

1. An electronic module for an anti-skid braking system for operatingthe brake control mechanism of a wheeled vehicle, comprising: firstmeans operative while the vehicle is in motion to provide a velocitysignal representative of the rotational velocity of at least one wheelof the vehicle; second means coupled to the first means and operative todetect decreases in the value of the velocity signal produced by thefirst means and to produce output signals corresponding to thedecreases; third means coupled to the second means and operative tocompare the value of each output signal produced by the second meanswith the value of a deceleration reference signal corresponding to apredetermined value of wheel deceleration indicating the imminence of awheel lock-up condition and to produce an output signal whenever thevalue of an output signal produced by the second means bears apredetermined relationship to the value of the deceleration referencesignal; deceleration means associated with the vehicle and operativewhen the vehicle decelerates at a rate less than a predetermined rate toproduce a first control signal and operative when the vehicledecelerates at a rate greater than the predetermined rate to produce asecond control signal; and load control means coupled to the third meansand to the deceleration means and having an output connection adapted tobe coupled to the brake control mechanism of the vehicle, said loadcontrol means being operative in response to an output signal producedby the third means and in response to a first control signal produced bythe deceleration means to produce and apply to the output connectionthereof a first train of output pulses having a first repetition rate,and operative in response to an output signal produced by the thirdmeans and in response to a second control signal produced by thedeceleration means to produce and apply to the output connection thereofa second train of output pulses having a second repetition rate.
 2. Ananti-skid braking system in accordance with claim 1 wherein: thedeceleration means includes a decelerometer.
 3. An electronic modulE inaccordance with claim 1 wherein: the load control means includes adual-rate multivibrator circuit.
 4. An electronic module in accordancewith claim 1 wherein the load control means includes: input meanscoupled to the third means and operative to receive each output signalproduced by the third means, said input means being operative inresponse to each output signal produced by the third means to produce acorresponding output signal of a predetermined duration; and dual-ratemultivibrator circuit means coupled to the input means and to thedeceleration means and operative to receive each output signal producedby the input means and the first and second control signals produced bythe deceleration means, said dual-rate multivibrator circuit means beingoperative in response to an output signal produced by the input meansand a first control signal produced by the deceleration means to producea first train of output pulses having a first repetition rate for theduration of the output signal produced by the input means, and operativein response to an output signal produced by the input means and a secondcontrol signal produced by the deceleration means to produce a secondtrain of output pulses having a second repetition rate for the durationof the output signal produced by the input means.
 5. An electronicmodule in accordance with claim 4 wherein: the deceleration meansincludes a decelerometer.
 6. An electronic module in accordance withclaim 5 wherein the load control means further includes: output meanscoupled to the input means and to the dual-rate multivibrator circuitmeans and operative to receive each output signal produced by the inputmeans and each train of output pulses produced by the dual-ratemultivibrator circuit means, said output means being operative inresponse to each output signal produced by the input means and a trainof output pulses produced by the dual-rate multivibrator circuit meansto invert and apply the train of output pulses to an output connection.7. An electronic module in accordance with claim 1 wherein: the wheel ofthe vehicle is a rear wheel of the vehicle; and the first means includesa wheel velocity-sensing means associated with the rear wheel of thevehicle and operative while the vehicle is in motion to produce a pulsetrain having a frequency varying in direct proportion to the rotationalvelocity of the rear wheel.
 8. An electronic module in accordance withclaim 7 wherein: the first means further includes means coupled to thewheel velocity-sensing means and operative to convert the pulse trainproduced by the wheel velocity-sensing means into a dc velocity signalhaving an amplitude varying in accordance with variations in thefrequency of the pulse train produced by the wheel velocity-sensingmeans.
 9. An electronic module in accordance with claim 7 wherein: thevehicle includes a drive shaft cooperating with the rear wheel of thevehicle; and the wheel velocity-sensing means comprises: a slotted discadapted to be fixedly mounted on the drive shaft of the vehicle andadapted to rotate with the drive shaft; a light source adapted to bearranged on one side of the slotted disc, said slotted disc operating tochop light produced by the light source at a frequency varying inaccordance with variations in the rotational velocity of the driveshaft; and a photoresponsive device on the other side of the slotteddisc in optical alignment with the light source and operative to receivethe light chopped by the slotted disc and to convert the chopped lightto a train of pulse signals having a frequency varying in accordancewith the variations in the rotational velocity of the drive shaft. 10.An electronic module for operating the brake control mechanism of awheeled vehicle, comprising: first means operative while the vehicle isin motion to provide a velocity signal representative of the rotationalvelocity of at least one Wheel of the vehicle; second means coupled tothe first means and operative to detect decreases in the value of thevelocity signal produced by the first means and to produce outputsignals corresponding to the decreases; velocity circuit means coupledto the first means and operative when the velocity signal produced bythe first means has a value greater than a predetermined valuecorresponding to a predetermined cutout velocity to produce an outputsignal; braking circuit means operative to produce an output signalwhenever the vehicle is being braked; third means coupled to the secondmeans and operative to compare the value of each output signal producedby the second means with the value of a deceleration reference signalcorresponding to a predetermined value of wheel deceleration indicatingthe imminence of a wheel lock-up condition and to produce an outputsignal whenever the value of an output signal produced by the secondmeans bears a predetermined relationship to the value of thedeceleration reference signal; gating means coupled to the velocitycircuit means, the braking circuit means, and to the third means andoperative to receive the output signals produced by said means, saidgating means being operative only in response to output signals producedby the velocity circuit means and the braking circuit means to gatetherethrough an output signal produced by the third means; decelerationmeans associated with the vehicle and operative when the vehicledecelerates at a rate less than a predetermined rate to produce a firstcontrol signal and operative when the vehicle decelerates at a rategreater than the predetermined rate to produce a second control signal;and load control means coupled to the gating means and to thedeceleration means and having an output connection adapted to be coupledto the brake control mechanism of the vehicle, said load control meansbeing operative in response to an output signal gated from the thirdmeans through the gating means and in response to a first control signalproduced by the deceleration means to produce and apply to the outputconnection thereof a first train of output pulses having a firstrepetition rate, and operative in response to an output signal gatedfrom the third means through the gating means and in response to asecond control signal produced by the deceleration means to produce andapply to the output connection thereof a second train of output pulseshaving a second repetition rate.
 11. An anti-skid braking system inaccordance with claim 10 wherein: the deceleration means includes adecelerometer.
 12. An electronic module in accordance with claim 10wherein: the load control means includes a dual-rate multivibratorcircuit.
 13. An electronic module in accordance with claim 10 whereinthe load control means includes: input means coupled to the third meansand operative to receive each output signal produced by the third means,said input means being operative in response to each output signalproduced by the third means to produce a corresponding output signal ofa predetermined duration; and dual-rate multivibrator circuit meanscoupled to the input means and to the deceleration means and operativeto receive each output signal produced by the input means and the firstand second control signals produced by the deceleration means, saiddual-rate multivibrator circuit means being operative in response to anoutput signal produced by the input means and a first control signalproduced by the deceleration means to produce a first train of outputpulses having a first repetition rate for the duration of the outputsignal produced by the input means, and operative in response to anoutput signal produced by the input means and a second control signalproduced by the deceleration means to produce a second train of outputpulses having a second repetition rate for the duration of the outputsignal produced by the input means.
 14. An eleCtronic module inaccordance with claim 13 wherein: the deceleration means includes adecelerometer.
 15. An electronic module in accordance with claim 13wherein the load control means further includes: output means coupled tothe input means and to the dual-rate multivibrator circuit means andoperative to receive each output signal produced by the input means andeach train of output pulses produced by the dual-rate multivibratorcircuit means, said output means being operative in response to eachoutput signal produced by the input means and a train of output pulsesproduced by the dual-rate multivibrator circuit means to invert andapply the train of output pulses to an output connection.